Dissertations / Theses on the topic 'Non-noble catalyst'

Two major obstacles currently limit the commercial viability of proton exchange membrane fuel cells (PEMFCs): cost and operating life. The most important contribution to the high cost of these systems is the use of platinum (Pt) as a catalyst, especially on the cathode where the oxygen reduction reaction (ORR) takes place. This thesis is part of the intensive international research efforts to find an alternative substitute for platinum. Doped carbon nanomaterials have been identified as a potential replacement for platinum ORR-electrocatalyst due to their excellent electrical conductivity and chemical resistance in acidic and basic environments. By doping the carbon nanomaterials with nitrogen, in the preferred pyridinic and quaternary forms, iron can be coordinated to complete the catalytic sites on an atomic scale. Nanocrystalline powder has recently been developed in the Plasma Processing Laboratory (PPL) at McGill University. The particles constituting the powder, in the form of graphene nanoflakes (GNFs), are formed by the superposition of ten graphene layers on average and have a spatial extension on the order of hundreds of nanometers. These planes have many terminating edges upon which nitrogen can be incorporated due to their high reactivity. The crystallinity also leads to a highly stable material paving the way for a promising catalyst replacement in the PEMFC.The objective of this thesis is to take these crystalline GNFs and dope them with nitrogen in high quantities on the edges of the graphene planes in pyridinic and quaternary forms to create the catalytic sites necessary for ORR. An inductively-coupled thermal plasma (ICP) is used to dissociate methane at very high temperatures, with homogeneous GNF nucleation commencing shortly after by way of rapid quenching. Nitrogen doping occurs in a second treatment phase by manipulating plasma conditions in order to create excited and dissociated nitrogen species that react at the edges of the GNFs.Nitrogen doping up to 33.4 at.%Ntotal has been demonstrated, which bests any other nitrogen-doped graphene by at least a factor of 2.6 and even the best nitrogen-doped carbonaceous material by 67%. Pyridinic and quaternary nitrogen constitute 8.2 at.%Npyrid and 4.9 at.%Nquat, respectively. This has been done whilst maintaining the crystalline structure and without introducing defects or impurities that would otherwise affect crystallinity and durability of these materials in future potential applications. Sequential in-situ GNF synthesis and deposition/dispersion onto a carbon cloth, which functions as the gas diffusion layer (GDL) in fuel cells, has also been demonstrated. Solid anchoring of the deposited GNFs on the individual carbon fibers is observed, and columnar growth with open film porosity reveals GNF films of micrometer-scale thicknesses. These films also exhibit desirable properties required for the ORR: porosity, homogeneity over a large area, good contact to the electrical transport throughout the network of particles and accessibility to the catalytic sites. The obtained properties seem in fact unmatched by catalytic particle ink applications commonly used in the manufacture of the catalyst layer. This in-situ work is promising and original, establishing a potential new method of producing membrane electrode assemblies (MEAs) in PEM fuel cell manufacturing.This new graphene nanomaterial could also pave the way for its potential use in supercapacitors, solar cells, biosensors, batteries, fuel storage, field-effect transistors, filtration and electrochemical devices, in addition to the fuel cell catalysis applications under study.
Deux obstacles majeurs limitent présentement la viabilité commerciale des piles à combustibles à membrane électrolyte polymérique (PEMFC), leurs prix et durée d'opération. La contribution la plus importante au coût élevé de ces systèmes est l'utilisation du platine (Pt) en tant que catalyseur, en particulier au niveau de la réaction de réduction de l'oxygène (ORR). Une activité de recherche intense à l'échelle internationale est en cours pour trouver une alternative de remplacement pour le platine; cette thèse s'inscrit dans cet effort. Certains matériaux tels les nanostructures à base de carbone fonctionalisées semblent prometteurs en tant que catalyseur pour la réaction ORR, en particulier de par leur bonne conductivité électrique et leur résistance à la dégradation en milieux acides ou alkalins. Les sites catalytiques dans ces matériaux sont établis par une fonctionalization spécifique à l'azote sur laquelle une coordination d'atomes de fer est ajoutée, formant ainsi des sites catalytiques dispersés à l'échelle atomique. Une poudre nanocrystalline a récemment été développée au Laboratoire de procédés plasmas (LPP) de l'Université McGill. Les particules formant cette poudre ont la forme de nanoflocons de graphene (NFG) formés par la superposition d'une dizaine de plans de graphène en moyenne, et ayant une extension spatiale de l'ordre de la centaine de nanomètres. Les bords de ces plans ont la réactivité et la structure nécessaire pour incorporer des fonctionalités à l'azote tout en maintenant la cristallinité des plans intacte. La grande cristallinité de ces matériaux leur donne une très bonne résistance à la corrosion et au milieux acide des PEMFC, et en font un candidat prometteur pour remplacer le platine.L'objectif de cette thèse et d'insérer une quantité important de fonctionalization à l'azote de forme pyridinique et quaternaire sur les bords des NFG afin de créer les sites catalytiques nécessaires pour la réaction ORR. Un plasma thermique à couplage inductif (ICP) est utilisé pour la dissociation du méthane à haute température, suivi d'une nucléation homogène des NFG dans les zones de trempe rapide du jet de plasma. La fonctionalization à l'azote est effectuée dans une deuxième phase du traitement en modifiant les paramètres d'opération du plasma afin de mettre à profit les espèces exitées et dissociés d'un plasma d'azote.Une fonctionalization à l'azote jusqu'à 33.4 at.%Ntotal est obtenue dans ce projet, cette valeur étant 2.6 fois supérieure au meilleur résultat obtenu dans la littérature pour le graphène fonctionalizé à l'azote, et même 67% supérieure au meilleur matériau carboné avec fonctionalité azote. Les fonctionalités à l'azote pyridinique et quaternaire constituent respectivement 8.2 at.%Npyrid et 4.9 at.%Nquat. Ces résultats sont obtenus en maintenant la structure NFG intacte, en particulier en maintenant leur crystallinité et sans l'introduction de défauts de structure ou d'impuretés pouvant diminuer la performance du matériau au niveau des applications. Une déposition in situ des NFG à l'intérieur du réacteur de synthèse sur une membrane de carbone telle qu'utilisée dans les piles à combustible a également été démontrée. Un bon ancrage du dépôt de NFG est observé sur la membrane, et une croissance colonnaire avec porosité ouverte du film montre des épaisseurs du film de NFG de l'ordre du micromètre. Ces films montrent également les propriétés requises pour la RRO, soit la porosité, l'homogénéité sur une grande surface, un bon contact dans tout le réseau de particules pour le transport électrique, et l'accessibilité aux sites catalytiques. Les propriétés obtenues semblent en fait inégalée par les encres de particules catalytiques utilisées couramment pour la fabrication de la couche catalytique. Cette déposition in situ semble donc prometteuse et originale pour établir une nouvelle méthode de production de l'assemblage membrane-électrodes dans la fabrication des piles à combustibles du type PEM.

One of the goals in catalyst research for proton exchange membrane fuel cells (PEMFCs) is to find a cost-efficient alternative to platinum. Due to sluggish kinetics, the major requirement of the platinum comes from the catalyst layer used for the oxygen reduction reaction (ORR). Functionalized carbon nanomaterials present themselves as good candidates for the replacement of platinum due to their low cost, excellent electrical conductivity, and chemical resistance to acidic and basic environments. In this work, graphene nanoflakes (GNFs), which are nanopowders consisting of stacked graphene sheets, were used to support atomic iron as a non-noble metal catalyst. In the first stage of the study the iron-based catalyst was synthesized. Synthesis steps include the production of GNFs in methane plasma, adsorption of ferric acetate, and pyrolysis in ammonia-rich atmosphere. The catalyst structure was characterized at various stages throughout the synthesis steps and it was found that 0.28 atomic percent of iron could successfully be incorporated onto the surface. However, the synthesis method employed caused a general decrease to all calculated crystallinity parameters: purity decreased by 28%, crystallite size decreased by a factor of 2, and the average length of graphene plane decreased by a factor of 4. Characterization was also performed on the catalyst layer after it had been exposed to the PEMFC environment, revealing that the crystallinity parameters actually improved with respect to exposure time: after 100 hours purity increased by 32%, crystallite size increased by 25%, and the average length of graphene plane increased by 107%. Exposure to the PEMFC environment repairs the damage done to the original GNFs during the synthesis steps. The synthesized catalyst was used in the catalyst layer for the ORR of a PEMFC with a 1 cm2 active surface. A current of 150 mA/cm2 was observed at an applied voltage of 0.5 Volts with a catalyst loading of 1 mg. When the current is normalized with respect to the amount of metal present, the result of 11.8 A/mg of metal catalyst from the present catalyst out-performs most platinum-based catalysts being used in industry; current platinum catalyst have values ranging from 3 to 14 A/mg of platinum. In stability experiments, no losses were observed at the end of 100-hours long experiments performed at an applied voltage of 0.5 Volts. This represents a great improvement over comparable iron-based catalysts, which show a 45% loss under identical test conditions. The increased stability of the catalyst support structure demonstrates the advantage of the high crystallinity and large crystalline lengths of the GNFs in comparison to other commercial carbon blacks.
Un des objectifs de la recherche sur les catalyseurs pour les piles à combustible à membrane électrolyte polymérique (PCMEP) est de trouver une alternative moins coûteuse au platine. En raison d'une cinétique lente, le platine est surtout utilisé dans la couche de catalyseur au niveau de la cathode pour la réaction de réduction de l'oxygène (RRO). Les nanomatériaux de carbone fonctionnalisés se présentent comme de bons candidats pour le remplacement du platine en raison de leur faible coût, d'une excellente conductivité électrique et d'une résistance chimique aux milieux acides et basiques. Dans ce travail, les nanoflocons de graphène (NFG) constitués en moyenne d'une dixaine de plans de graphène empilées, ont été utilisés comme support aux atomes de fer pour créer un catalyseur métallique non noble. Lors d'une première étape, le catalyseur à base de fer a été synthétisé. Les étapes de synthèse comprennent la production des NFG dans le plasma de méthane, l'adsorption de l'acétate ferrique, et la pyrolyse dans une atmosphère riche en ammoniac. La structure du catalyseur a été caractérisée tout au long des étapes de synthèse, et il a été constaté qu'un pourcentage de 0,28 % en atomes de fer ont été incorporé aux structures NFG. Cependant, la méthode de synthèse utilisée a provoqué une baisse générale de tous les paramètres cristallins calculés: la pureté a diminué de 28%, la taille des cristallites a diminué d'un facteur 2, et la taille moyenne des plans de graphène d'un facteur 4. La caractérisation a été également effectuée sur la couche de catalyseur après avoir été exposée à l'environnement PCMEP, révélant que les paramètres cristallins sont effectivement améliorés avec la durée d'exposition. Au bout de 100 heures, la pureté a augmenté de 32%, la taille des cristallites de 25%, et la taille moyenne des plans de graphène de 107%. L'exposition à l'environnement de PCMEP a réduit les dommages causés aux NFG pendant les étapes de synthèse. Le catalyseur synthétisé a été utilisé pour la RRO dans un PCMEP avec une surface active de 1 cm2. Un courant de 150 mA/cm2 a été observé pour une tension appliquée de 0,5 volts et une masse de catalyseur de 1 mg. Lorsque le courant est normalisé par rapport à la quantité de métal présent, le résultat de 11,8 A/mg de métal surpasse les catalyseurs à base de platine les plus utilisés dans l'industrie. Les catalyseurs au platine ont des valeurs allant de 3 à 14 A/mg de platine. Dans les expériences de stabilité, pour une tension appliquée de 0,5 Volts, aucune perte de courant n'a été observée à la fin des 100 heures de l'expérience. Cela représente une grande amélioration par rapport aux autres catalyseurs à base de fer, qui montrent une perte de 45% dans des conditions expérimentales identiques. La stabilité accrue de la structure du catalyseur démontre l'avantage d'utiliser des NFG par rapport à d'autres nanomatériaux de carbone, grâce à leurs cristallinité élevée et leurs grandes longueurs cristallines.

El present treball es basa en l'estudi de la modificació de la superfície del negre de carboni (NC) per mitjà de tècniques de plasma. Tot i que aquest tipus de tractament s'utilitza de manera comú sobre superfícies planes, tanmateix encara existeixen problemes a l'hora de treballar en materials en pols degut a la dificultat que suposa la seva manipulació. En aquest treball s'ha modificat NC tant per tècniques de plasma a baixa pressió com per mitjà de tècniques de plasma atmosfèric. Per tal d'assolir aquest objectiu s'han posat a punt tres reactors de plasma capaços de modificar aquest tipus de material; dos reactors treballen a baixa pressió mentre que el tercer es tracta d'un equip a pressió atmosfèrica.

Els sistemes de plasma a baixa pressió utilitzats han estat un reactor down-stream i un reactor de llit fluiditzat. Ambdós sistemes utilitzen un generador de radio freqüències a 13,56MHz per tal de general el plasma. Tots dos sistemes han estat optimitzats per la modificació de materials en pols. En el cas del reactor down-stream, s'ha estudiat a posició d'entrada del gas reactiu, la potència del generador i el temps de modificació per a tres tipus de tractament: oxigen, nitrogen i amoníac. En el cas del reactor de llit fluiditzat, els paràmetres que s'han estudiat han estat la distància entre la pols i la zona de generació de plasma, la mida de la partícula i la porositat de la placa suport.

Pel que fa a la modificació mitjançant la utilització de plasma atmosfèric, s'ha dissenyat un sistema que permet utilitzar una torxa de plasma atmosfèric comercial (Openair® de Plasmatreat GmbH) per tal de modificar materials en pols. Aquest sistema consisteix en un reactor adaptable a la torxa de plasma atmosfèric on té lloc la modificació, un sistema d'introducció de la pols dins de la zona de reacció així com també un sistema de refredament i col·lecció del material modificat que conjuntament permeten un funcionament quasi-continu del tractament.

S'ha utilitzat el reactor down-stream i el reactor a pressió atmosfèrica per tal de modificar tres tipus diferents de negre de carboni (N134, XPB 171 i Vulcan XC-72). D'altra banda, s'ha grafititzat i extret el N134 prèviament a la modificació per tal de realitzar un estudi sobre la influència de l'estructura superficial així com també de la presència d'impureses sobre la superfície del NC. L'oxidació i l'augment de nitrogen en superfície han estat les dues modificacions que s'han estudiat principalment per tal de comparar el resultat obtingut per les tècniques presentades.

El NC s'ha caracteritzat mitjançant diverses tècniques analítiques per tal de poder obtenir informació sobre els canvis produïts durant la modificació per plasma. Aquestes tècniques inclouen superfície específica, XRD, WAXS, STM per tal d'estudiar els canvis en la seva morfologia i estructura de la superfície. D'altra banda, per tal d'estudiar els canvis en la composició química s'han emprat mesures de pH, valoracions àcid/base i XPS.

Finalment, alguns dels negres de caboni modificats han estat seleccionats per tal de ser avaluats en aplicacions finals tal i com són el reforçament d'elastòmers i la seva activitat vers la reducció d'oxigen utilitzada en les PEMFC per tal d'eliminar els metalls nobles. En el primer cas, s'ha estudiat l'efecte sobre la cinètica i el mecanisme de vulcanització del negre de carboni modificat mitjançant el plasma atmosfèric. Aquest estudi s'ha dut a terme utilitzant dues tècniques complementaries com són les corbes reomètriques i la vulcanització de molècules model (MCV). També s'han realitzat mesures d'adsorció de polímer sobre el NC i Bound Rubber per tal d'estudiar la interacció polímer-càrrega la qual presenta una gran influència en les propietats finals dels materials. D'altra banda, s'ha estudiat també la capacitat del NC modificat vers a la reducció d'oxigen a partir de voltametria cíclica i s'han determinat les propietats del NC que poden influir de manera rellevant en l'activitat cataítica final del NC per a aquesta reacció. Tot i que es necessari fer una preparació posterior al tractament de plasma per a aquesta aplicació, el material final pot contribuir notablement a la eliminació de metalls nobles com a catalitzadors de reducció d'oxigen en les Piles de Combustible.
The present works deals with plasma modification of carbon black (CB). Although this type of treatment is widely used on flat surfaces handling problems should be overcome in order to treat powders as CB. In this study CB has been modified both by means of low-pressure and atmospheric pressure non-equilibrium plasmas. In order to accomplish this objective three different plasma reactors have been set-up; two at low pressure and one at atmospheric pressure working conditions.

Low pressure plasma reactors utilised in this work consist in a down-stream and a fluidised bed system working at Radio Frequency generation power (RF 13,56 MHz). Both reactors have been optimized to treat powder materials. For the down-stream reactor, position of the reactive gas inlet, and treatment conditions such as generator power and time have been studied for oxygen, nitrogen and ammonia treatments. For the fluidized bed reactor the distance of the powder sample to the plasma generation zone, particle size and support porosity have been taken into account.

Concerning atmospheric plasma, a device has been set up in order to adapt a commercial plasma torch (Openair® from Plasmatreat GmbH), for powder modification. An adaptable reactor, a method to introduce the powder in the plasma zone as well as a collecting system had been developed in order to obtain a quasi-continuous modification treatment.

Three types of CBs, N134, XPB 171 and Vulcan XC-72 have been modified in both the down-stream and the atmospheric plasma system. Graphitization and extraction of N134 were also carried out before plasma modification in order to study the effect of both impurities and surface structure of the CB during plasma modification. Surface oxidation and nitrogen enrichment were the two main studied treatments in both systems which allowed comparing their performances.

Unmodified and Modified CBs have been characterised from several points of view. Specific surface area, XRD, WAXS and STM have been used in order to study morphological and surface structure changes. On the other hand, pH measurements, acid/base titration and XPS were employed in order to study the surface chemistry composition changes that had taken place during plasma modification.

Some of the modified CB grades were selected in order to be tested in final applications such as rubber reinforcement and oxygen reduction non-noble metal catalyst for PEMFC. In the first case, the effect of atmospheric plasma treatment on the vulcanization kinetics and mechanism has been evaluated both by rheometre curves and the model compounding approach. Studies about the polymer-filler interaction have been also carried out by calculating bound rubber and adsorption from polymer solution. Last but not least, plasma modification capacity to enhance the oxygen reduction activity to obtain non-noble metal catalysts for PEMFC has been evaluated after the correspondent preparation. Oxygen reduction activity has been studied by means of cyclic voltammetry. The main CB properties which could play an important role in such applications have been analyzed.

Ce travail porte sur la préparation et la caractérisation de catalyseurs bimétalliques Cu-Zn, Ni-Zn et Fe-Zn supportés sur TiO2 avec des rapports atomiques variables et sur l'étude de leurs propriétés catalytiques pour l'hydrogénation sélective d'hydrocarbures polyinsaturés. Les méthodes de co-dépôt-précipitation à l'urée (DPu) et co-dépôt-précipitation à pH fixe (DP8) ont été utilisées pour la préparation des matériaux. Les ions métalliques se déposent séquentiellement sur la surface de TiO2 (selon la séquence CuII < ZnII ?FeII
This work investigates the preparation and characterization of titania-supported non-noble bimetallic Cu-Zn, Ni-Zn and Fe-Zn catalysts with various atomic ratios and their catalytic properties for the selective hydrogenation of polyunsaturated hydrocarbons. Co-deposition-precipitation with urea (DPu) and co-deposition-precipitation at fixed pH (DP8) methods were employed for the samples preparation. The metal ions were sequentially deposited onto the TiO2 surface (the sequence of pH for ions deposition being CuII < ZnII ≈FeII < NiII) during the DPu, while they were simultaneously deposited using DP8 method. After sample reduction at proper temperature (350 °C for Cu-Zn, 450 °C for Ni-Zn and 500 °C for Fe-Zn), XRD and STEM-HAADF coupled with EDS showed that bimetallic nanoparticles were formed in Cu-Zn/TiO2 (Cu3Zn1 or Cu0.9Zn0.1 alloy) and Ni-Zn systems (Ni1Zn1 or Ni4Zn1 alloy) with average particle size smaller than 5 nm. Only metallic Fe was detected by XRD in Fe-Zn/TiO2. Zn is inactive for butadiene selective hydrogenation, and acts as a modifier of the monometallic catalysts whose activity follows the sequence: Cu < Fe < Ni. The addition of Zn slightly decreases the activity and influences the selectivity to butenes, but provides much more stable catalysts. The higher stability of the bimetallic catalysts was ascribed to the formation of lower amount of carbonaceous species during the reaction, resulting from the change in the size of the active metal surface ensembles by alloying with Zn

The aim of the study is to evaluate the ability of non-noble metal catalysts to function as the commercially used noble metal catalyst. The exhaust gas that was used in the project is generated from a heater developed by ReformTech AB with diesel as fuel. The compound that was focused on is carbon monoxide that has a concentration of 300-750 ppm. The catalysts that were tested are MnO/CeO2, CuO/CeO2 and a Pt/CeO2 catalyst used to compare the non-noble metal catalyst with. The sensitivity against sulfur poisoning was also analyzed by mixing sulfur into the fuel. Analysis of the exhaust gas was done with a micro-GC and the catalysts were also analyzed with SEM before and after exposure of sulfur.   The manganese catalyst with a loading of 7 wt-% did not show any activity against carbon monoxide oxidation. The copper catalysts contained two different loadings of active material, 7 and 14 wt-% and monoliths with 400 and 600 cpsi were used. Both loadings showed good activity against carbon monoxide oxidation.   The most prominent catalyst was the 14 wt-% CuO/CeO2 catalyst with a 600 cpsi monolith because of an increase in surface area. The SEM analysis showed that sulfur was present on the surface when the heater was using diesel with 300 ppm sulfur. The sulfur caused complete deactivation of the non-noble metal catalysts and a small decrease in activity was shown on the noble metal Pt catalyst.

Polymer electrolyte membrane fuel cells (PEMFC) are electrochemical devices which can directly convert the chemical energy of a fuel (such as hydrogen or a low-molecular weight alcohol) and an oxidant (i.e. oxygen) into electrical energy with high efficiency. Moreover, due their low operating temperature, they are suitable for automotive or portable applications. However, the slow kinetics of oxygen reduction reaction (ORR) requires the use of costly Pt-based catalysts at the cathode in order to obtain the desired power density values. Nevertheless, the cathode is still responsible for the main voltage loss in the cell. The overall objective of the research carried out in this Ph.D. thesis was the development of Pt-free ORR catalysts starting from different carbon, nitrogen and transition metals precursors. Different synthesis approaches were used in order to obtain an improvement of the activity, and to understand the influence of the synthesis process variables. In particular, the influence of carbon supports (commercial and synthesized in the lab), nitrogen and transition metals precursors, templating agents, number and temperature of pyrolysis were examined. The catalysts produced were characterized by means of several instrumental techniques such as N2 physisorption, XRD, XPS, EDX, SEM, FESEM, TEM, Raman and FTIR. The effect of the presence of different transition metals on the pyrolysis process was investigated by TGA coupled with a mass spectroscopy analysis, in order to have an insight on their influence in the formation of ORR active sites. The activity toward ORR was assessed by RDE-RRDE (rotating disk electrode - rotating ring disk electrode) analysis and by gas-diffusion electrode in a 3-electrodes electrochemical cell configuration. The electrochemical techniques used were cyclic voltammetry (CV), linear sweep voltammetry (LSV), staircase voltammetry (SV), chronoamperometry and electrochemical impedance spectroscopy (EIS). These electrochemical tests were performed in both acid and alkaline conditions, with reference to the potential applications in both H+ and OH– conducing polymer electrolyte membrane fuel cells. This first part of research was carried out in the laboratories of the Gre.En2 (Green Energy and Engineering) Group in the Department of Applied Science and Technology (DISAT) at Politecnico di Torino. Then, in the second part, some of the most promising electrocatalysts in terms of ORR activity were in different types of single PEMFC. In particular, using acidic electrolyte membrane, the tests were performed using H2 or methanol as fuels. In the case of direct methanol fuel cell (DMFC) tests, short-term durability tests were done in order to compare the durability performance of our catalysts with a standard Pt-based catalysts. The tests with alkaline electrolyte membrane were performed using ethanol as fuel. This second part of research was carried out at the Universidad Autonoma de Madrid in the laboratories of the Department of Applied Physical-Chemistry. Here the structure of the thesis: Chapter 1 is a general introduction about the PEMFC fuel cell technology, particularly focusing on the non-noble metal catalysts for ORR as potential alternative to Pt. Chapter 2 is focused on the use of different types of reduced graphene oxide as support for the synthesis of Fe-N/C catalysts. In Chapter 3, a complex between Co ions and a N-containing ligand molecule is impregnated on multi walled carbon nanotubes and pyrolyzed one or two times for producing a Co-N-C catalyst, and the influence of the second pyrolysis on the activity improvement was investigated. Chapter 4 deals the optimization of the synthesis process of a Fe-N-C catalyst using polypyrrole as N source and mesoporous carbon a C-support. In Chapter 5 the study of the influence of different silica templates on the morphology on the ORR activity of a Fe-N-C catalyst synthesized using Fe-phthalocyanine as precursor is presented. In Chapter 6, different Me-phthalocyanines (Me = Fe, Co, Cu, Zn) were used as precursor for the synthesis of Me-N-C catalysts using SBA-15 silica as hard template. The influence of the different transition metals on the pyrolysis process and on the ORR activity and selectivity toward a complete 4 e- oxygen reduction was investigated in both acid and alkaline conditions. A detailed kinetic analysis in acid conditions is also presented. The most active catalyst was tested in different types of PEMFCs. Finally, in Chapter 7, the influence of four different carbon supports on the ORR activity of Fe-N/C catalysts in acid and alkaline conditions as well as the performance in single PEMFC is examined. The general conclusions of the thesis are presented in Chapter 8.

Today fuel cells are far from being common place in the commercial market, primarily due to their high cost. The cost of such a system is largely determined by the platinum based catalysts used at both the anode and cathode of the fuel cell. If a non-noble fuel cell electrocatalyst could be used at either of these electrodes, the cost of a fuel cell system would be drastically reduced. Highthroughput physical vapour deposition and the modification of single crystal surfaces, has been used to synthesise candidate non-noble electrocatalysts which were then screened to determine their activity. Amorphous tungsten carbide thin films were shown to be catalytically active towards both the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). The constituent elements were seen to be less active than the alloys. These results are consistent with the literature where it has also been seen that WC is active, with W2C showing poorer activity.1,2 The trend in current density with respect to alloy composition confirms the results in the literature, with the highest activity seen at compositions corresponding to the WC phase, and a local minima in activity seen at compositions corresponding to the W2C phase. Metastable and amorphous intertransition metal alloys of WCu are shown to catalyse both the HER and the HOR. The constituent metals again exhibit poor activity. The results are consistent with ab initio calculations predicting HER activity for Cu overlayers on W, with the detected changes of the density of states (DOS) at the Fermi level associated with alloy formation.3 Two maxima in the HER activity are observed as a function of composition. This activity is associated with a metastable phase at W20Cu80 and a second at W50Cu50. The alloy at 50 at% also shows a maximum in the HOR activity, whereas the phase at W20Cu80 is not HOR active. The W20Cu80 phase is found to beoxygen covered at the HOR potential, explaining its inactivity. These results highlight the potentials of developing non-noble metal alloy catalysts for hydrogen fuel cells.

Hydrogen is seen as the ‘energy carrier of the future’ due to the element’s relative abundance, the formation of water as opposed to the green house gases when utilised as a fuel in fuel cells, and the ability to be produced by electrolysers powered from renewable energy sources such as wind, water and sunlight. The development of hydrogen production through electrolysis is hindered by the high costs associated with the technology, specifically the ion exchange membranes and electrocatalysts that are employed in the membrane electrode assemblies used in polymer electrolyte electrolysers. This research focused on the development of non-noble catalysts suitable for hydrogen and oxygen evolution in alkaline electrolysis. Synthesis of NiO was achieved through thermal decomposition, chemical bath deposition and solution growth techniques. A mixed metal oxide, NiCo2O4, was synthesized through thermal decomposition of metal nitrate salts. Cyclic voltammetry and steady state electrochemical experiments on the electrodes were conducted in an electrochemical half cell electrolyser. A thin film of pure NiO was formed onto a titanium substrate through chemical bath deposition followed by thermal decomposition. The performance of the electrode at 1.73 V, relative to the mass of the catalyst loading, produced 0.25 A cm-2 mg-1 in 1 M NaOH at 25°C (IrO2 produced 0.44 A cm-2 mg-1 in the same electrolyser). The electrode’s performance is attributed to the nanoporous structure of the catalyst film (20 – 200 nm pore diameters), which was formed from the chemical bath deposition method used to prepare the catalyst films. Unfortunately this procedure has a limited film thicknesses so higher loadings could not be achieved. Higher loadings of other non-noble electrocatalysts were made possible with addition of a PVDF binder to the catalyst film. Physical analysis through XRD was performed on the most promising catalysts for the oxygen evolution reaction to confirm their composition. A blend of α-Ni(OH)2 and 4Ni(OH)2•NiOOH•xH2O formed through the chemical bath deposition technique produced higher current densities (104 mA cm-2 at 0.8 V vs. Hg/HgO) than another non-noble metal catalyst, NiCo2O4 (97 mA cm-2) II in 1 M NaOH at 25°C. An alkaline polymer electrolyser free from noble metals was developed with a membrane electrode assembly that utilised a partially fluorinated membrane, a PVBC/PVC ionomer in the catalyst layers, 1.0 mg NiMoO4 cm-2 in the cathode and 0.7 mg NiCo2O4 cm-2 in the anode. It produced 0.4 A cm-2 in 1 M KOH at 25° at a potential of 1.9 V.

Notre stratégie de développement «croissance à tout prix» a causé de nombreux problèmes environnementaux. Ainsi, la dépendance vis-à-vis des combustibles fossiles tels que le pétrole est encore plus élevée. On se doit de réduire cette dépendance. Parmi les stratégies permettant de réduire cette dépense on peut citer la production d'hydrogène, de gaz de synthèse ou d'autres produits utilisant du CO2 et/ou du CH4. L’utilisant de ces derniers est l'un des moyens prometteurs de convertir les gaz à effet de serre en produits chimiques est le procédé de reformage à sec du méthane. Ainsi, cette thèse vise à proposer de nouveaux supports utilisant de différents promoteurs pour améliorer la sélectivité et la stabilité des catalyseurs à base de nickel pour le reformage à sec du méthane ; et à analyser les performances catalytiques des catalyseurs préparés en associant les effets de température avec des caractérisations physico-chimiques telles que la mesure de surface, la diffraction des rayons X, et la désorption programmée à la température du CO2. Tout d'abord, différents promoteurs avec du nickel ont été imprégnés sur une argile naturelle ou de l’argile modifiée Fe/Cu de Tunisie. Deuxièmement, les catalyseurs dérivés de l'argile synthétique ont été préparés par une méthode de co-précipitation pour rechercher les influences de la structure sur le DRM. Enfin, les catalyseurs ayant la même composition que d'excellents catalyseurs dérivés de Ni-hydrotalcite ont été synthétisés mécaniquement par broyage planétaire pour comparer l'effet de la vitesse de rotation et de la préparation à des synthèses classiques
The development strategy of “growth-at-any-cost” has not been applied to the current development with the increased attention of various countries to environmental issues. But the dependence on fossil fuels such as petroleum will be still high in a short period of time based on the consideration of economic and social development. Thus, the focus on the production of hydrogen, syngas or other products using CO2 and/or CH4 that has attracted more attention in chemical products is the process of dry reforming of methane. Thus, this research focuses on proposing new supports loaded with different promoters to enhance the catalytic selectivity and stability of nickel-based catalysts for dry reforming of methane, and analyze the catalytic performance of prepared catalysts by associating temperature effects with multiple characterizations such as Brunauer-Emmett-Teller, X-ray diffraction, and CO2-temperature programmed desorption. First, different promoters with nickel are impregnated on natural clay or Fe/Cu-modified clay from Tunisia. Second, the synthetic clay derived catalysts are prepared by co-precipitation method to research the influences of structure on the DRM. In the end, the catalysts having the same composition as excellent Ni-hydrotalcite derived catalysts are further synthesized by ball milling to compare the effect of rotational speed and preparation

Polymer electrolyte fuel cells (PEFC) convert chemicalenergy into electrical energy with higher efficiency thaninternal combustion engines. They are particularly suited fortransportation applications or portable devices owing to theirhigh power density and low operating temperature. The latter ishowever detrimental to the kinetics of electrochemicalreactions and in particular to the reduction of oxygen at thecathode. The latter reaction requires enhancing by the verybest catalyst, today platinum. Even so, the cathode isresponsible for the main loss of voltage in the cell. Moreover,the scarce and expensive nature of platinum craves theoptimisation of its use.

The purpose of this thesis was to better understand thefunctioning of the porous cathode in the PEFC. This wasachieved by developing physical models to predict the responseof the cathode to steady-state polarisation, currentinterruption (CI) and electrochemical impedance spectroscopy(EIS), and by comparing these results to experimental ones. Themodels account for the kinetics of the oxygen reduction as wellas for the transport of the reactants throughout the cathode,i.e. diffusion of gases and proton migration. The agglomeratestructure was assumed for the description of the internalstructure of the cathode. The electrochemical experiments wereperformed on electrodes having a surface of 0.5 cm2 using alaboratory fuel cell.

The response of the cathode to various electrodecompositions, thickness, oxygen pressure and relative humiditywas experimentally investigated with steady-state polarisation,EIS and CI techniques. It is shown that a content in thecathode of 35-43 wt % of Nafion, the polymer electrolyte, gavethe best performance. Such cathodes display a doubling of theapparent Tafel slope at high current density. In this region,the current is proportional to the cathode thickness and to theoxygen pressure, which, according to the agglomerate model,corresponds to limitation by oxygen diffusion in theagglomerates. The same analysis was made using EIS. Moreover,experimental results showed that the Tafel slope increases fordecreasing relative humidity. For Nafion contents lower than 35wt %, the cathode becomes limited by proton migration too. ForNafion contents larger than 40 wt %, the cathode performance athigh current density decreases again owing to an additionalmass transport. The latter is believed to be oxygen diffusionthroughout the cathode. The activity for oxygen reduction ofcatalysts based on iron acetate adsorbed on a carbon powder andpyrolysed at 900°C in ammonia atmosphere was alsoinvestigated. It was shown that the choice of carbon has atremendous effect. The best catalysts were, on a weight basis,as active as platinum.

Keywords:polymer electrolyte fuel cell, cathode, masstransport, porous electrode, modelling, agglomerate model,electrochemical impedance spectroscopy, current interrupt,transient techniques, non-noble catalysts

Este trabalho teve como objetivo investigar eletrocatalisadores de baixo custo à base de carbeto de tungstênio, carbono e ferro submetidos a diferentes processos de nitretação quanto à atividade catalítica para reação de redução do oxigênio (RRO) nos eletrólitos ácido e alcalino. Os catalisadores foram divididos em três séries distintas, a primeira compreendendo aqueles onde houve variação da carga de carbeto de tungstênio em relação ao suporte de carbono, que foram impregnados com o complexo Fe2+(2,4,6-Tris(2-piridil)-1,3,5-Triazina)2, [Fe(TPTZ)2]2+ e tratados em duas temperaturas diferentes, 700 e 800 oC em atmosfera de nitrogênio. Na segunda série foi mantida constante a carga de carbeto de tungstênio (30% de W/C, m/m) sendo que esta mescla foi preparada usando carbonos dopados previamente com três fontes distintas de nitrogênio (HNO3, NH3 e HNO3/NH3); isto foi seguido pela incorporação do complexo Fe[TPTZ]2+ e pelos mesmos tratamentos térmicos acima mencionados. Na terceira série, os eletrocatalisadores foram preparados com três tipos de carbonos (Vulcan, Ketjenblack e Monarch), aos quais foi incorporado o complexo Fe[TPTZ]2+, seguido pelo tratamento térmico a 800 °C em atmosfera de nitrogênio e então por dopagem com amônia a 950 °C. As três séries de eletrocatalisadores sintetizados neste trabalho foram cuidadosamente caracterizadas por espectroscopia infra-vermelho e UV-Visível, difratometria de raio-x, microscopia eletrônica de transmissão, energia dispersiva de raios-x, espectroscipia Raman, espectroscopia fotoeletrônica de raios-x. As investigações eletroquímicas foram realizadas por voltametria cíclica (VC) e pelo levantamento de curvas de polarização de estado estacionário para a RRO, usando a técnica de eletrodo de disco/anel rotatório, com materiais catalíticos formando filmes finos depositados no eletrodo de disco. Nas três séries de catalisadores foram desenvolvidos materiais com bom desempenho para a RRO. Nos estudos da primeira série de catalisadores, notou-se que o material mais ativo foi aquele formado por WC-FeNx/C com 30 % de W/C e 5% de Fe pirolisado a 800 °C. Na segunda série foi observado que os desempenhos dos catalisadores variaram de acordo com o tipo de protocolo de nitretação, presença de ferro e temperatura de tratamento térmico. Em eletrólito alcalino, os eletrocatalisadores apresentaram maiores desempenhos, que resultaram bastante próximos em relação ao do catalisador de Pt dispersa em carbono usado como referência. Na terceira série de eletrocatalisadores investigados, verificou-se que o melhor desempenho obtido foi com o catalisador com carbono Monarch com amônia, cuja atividade catalítica resultou superior à dos demais, devido ao maior número de estruturas ativas FeNx e N/C formadas pelo tratamento com amônia. Os resultados nos meios ácido e alcalino para a primeira e segunda séries de eletrocatalisadores sugerem a ocorrência de um mecanismo indireto (2e- + 2e-), ou seja, em meio ácido (alcalino) primeiro o O2 reduz para H2O2 (HO2 ) e depois de H2O2 (HO2 ) para H2O. Os sítios predominantemente envolvidos na catálise da reação são WC e FeNx em meio ácido e WC e N/C em meio alcalino. Finalmente, para a terceira série de eletrocatalisadores o mecanismo reacional em meio ácido envolve um mecanismo direto de 4e-, com participação importante dos sítios ativos de Fe-N2.
This work aims to investigate low cost electrocatalysts based on tungsten carbide, carbon and iron submitted to different nitriding processes for the catalytic activity for the oxygen reduction reaction (ORR) in acid and alkaline electrolytes. The catalysts were divided into three distinct series, the first one comprising those with different tungsten carbide loads with respect to the carbon support, which were impregnated with the Fe2+ (2,4,6-Tris (2-pyridyl) - 1,3,5-triazine)2, [Fe (TPTZ)]2+, complex and treated at two different temperatures, 700 and 800 oC in nitrogen atmosphere. In the second series, the tungsten carbide load (30% W/C, m/m) was kept constant but this mixture was prepared using previously doped carbons using three different sources of nitrogen (HNO3, NH3 and HNO3/NH3); this was followed by the incorporation of the Fe[TPTZ]2+ complex and by the same heat treatments as mentioned above. In the third series, the electrocatalysts were prepared with three carbon types (Vulcan, Ketjenblack and Monarch), to which the Fe[TPTZ]2+ complex was added, followed by heat treatment at 800 °C under nitrogen and then by nitriding using a flow of ammonia at 950 °C. The three series of electrocatalysts synthesized in this work were carefully characterized by infra-red and UV-Visible spectroscopy, x-ray diffraction, transmission electron microscopy, x-ray energy dispersive, Raman spectroscopy, x-ray photoelectron spectroscopy. The electrochemical investigations were performed by cyclic voltammetry (CV) and by measurements of steady-state polarization curves for ORR using rotating ring-disc electrode technique, with catalytic materials forming thin films deposited on the disc. In the three catalyst series, materials with good performance for the ORR were developed. In the studies of the first series of catalysts, it was seen that the most active material was that formed by WC-FeNx/C with 30%W/C and 5% Fe pyrolyzed at 800 ° C. In the second series it was observed that the performances of the catalysts varied according to the type of nitriding protocol, presence of iron and temperature of heat treatment. The electrocatalysts showed higher performances in alkaline electrolyte, which were very close to that of a reference Pt/C catalyst. In the third series of electrocatalysts, the best performance was obtained with the Monarch carbon catalyst heat-treated with ammonia, whose catalytic activity was higher than all others, due to the greater number of FeNx and N/C active structures formed by the treatment with ammonia. The results in acidic and alkaline conditions for the first and second series of electrocatalysts suggest the occurrence of an indirect ORR mechanism (2e- + 2e-), that is, in acid (alkaline) media first O2 is reduced to H2O2 (HO2) followed by the reduction of H2O2 (HO2). The active sites predominantly involved in the reaction electrocatalysis are WC and FeNx in acid media and WC e N/C in alcaline media. Finally, for the third series of electrocatalysts, the acidic reaction involves a direct 4e- mechanism, having important participation of the Fe-N2 active sites.

[ES] En este trabajo estudiamos dos reacciones catalíticas relevantes para la industria y la localización del anión fluoruro en la zeolita RTH, sintetizada en medio fluoruro. El capítulo 3 es el primer capítulo de resultados, donde se estudia la reducción quimioselectiva del nitroestireno en las superficies Ni(111), Co(111), Cu(111) y Pd(111). El mecanismo generalmente aceptado de esta reacción está basado en el esquema propuesto por Haber en 1898, en el que la reacción puede transcurrir por dos rutas, la directa y la de condensación. En este capítulo exploramos ambas rutas, y observamos que la ruptura de los enlaces N-O y la consecuente formación de enlaces metal-O está más favorecida que la formación de enlaces N-H en las superficies Ni(111) y Co(111), debido al carácter oxofílico de ambos metales. Las etapas más lentas involucran la formación de enlaces N-H. En las superficies de metales nobles como Pt(111) y Pd(111) se observa el comportamiento contrario. La superficie Cu(111) es un caso intermedio comparado con los metales nobles y no nobles. Además, el nitroestireno interactúa con los átomos de Cu de la superficie solo a través de grupo nitro, con lo cual es un candidato ideal para alcanzar selectividades cerca del 100%. Sin embargo, la superficie Cu(111) no es capaz de activar la molécula de H2. En este sentido, proponemos un catalizador bimetálico basado en Cu, dopado con otro metal capaz de activar al H2, tales como el Pd o el Ni. En los capítulos 4 y 5 se ha estudiado la reducción catalítica selectiva de los óxidos de nitrógeno (SCR, en inglés) con amoníaco. Usando métodos de DFT, hemos encontrado rutas para la oxidación de NO a NO2, nitritos y nitratos con energías de activación relativamente bajas. También, hemos encontrado que la reducción de Cu2+ a Cu+ requiere la participación simultánea de NO y NH3. Posteriormente, hemos estudiado la influencia del NH3 en este sistema con métodos de dinámica molecular. El NH3 interacciona fuertemente con el Cu+ de forma que dos moléculas de este gas son suficientes para romper la coordinación del catión Cu+ con los oxígenos del anillo 6r, y formar el complejo lineal [Cu(NH3)2]+. Además, los cationes Cu2+ pueden ser estabilizados fuera de la red mediante la formación del complejo tetraamincobre(II). Debido a la presencia de los cationes Cu+ y Cu2+ coordinados a la red de la zeolita, aparecen bandas en la región entre 800-1000 cm-1 del espectro infrarrojo. El análisis de las frecuencias IR de varios modelos con Cu+ y Cu2+ coordinados al anillo 6r, o formando complejos con amoniaco indica que cuando los cationes Cu+ y Cu2+ están coordinados a los oxígenos del anillo 6r aparecen vibraciones entre 830 y 960 cm-1. Frecuencias en esta zona también se obtienen en los casos en que NO, NO2, O2 y combinaciones de dos de ellos están adsorbidos en Cu+ y Cu2+. Sin embargo, cuando los cationes Cu+ y Cu2+ están fuera del anillo (no hay enlaces entre los cationes de cobre y los oxígenos del anillo 6r) no se obtienen vibraciones de IR en esta región del espectro. Estos resultados indican que con el seguimiento del espectro IR durante la reacción SCR es posible determinar si los cationes Cu+ y Cu2+ están coordinados o no al anillo de 6r en las etapas de oxidación y reducción. Por último, hemos simulado el desplazamiento químico de 19F, δiso,, en la zeolita sintetizada RTH. El análisis del δiso de los distintos modelos utilizados nos ha permitido reconocer la simetría del material sintetizado, el cual pertenece al grupo espacial P1 y la nueva celda unidad ha sido confirmada experimentalmente por difracción de rayos X. Finalmente, hemos asignado la señal experimental que aparece en el espectro de 19F a -67.2_ppm, al F- localizado en un sitio T2, el cual es a su vez la posición más estable. Además, la señal a -71.8 ppm se ha asignado al anión F- localizado en un sitio T4.
[CA] En aquest treball estudiem dues reaccions catalítiques rellevants per a la indústria i la localització de l'anió fluorur en la zeolita RTH, sintetitzada al mig fluorur. El capítol 3 és el primer capítol de resultats, on s'estudia la reducció quimioselectiva del nitroestireno en les superfícies Ni(111), Co(111), Cu(111) i Pd(111). El mecanisme generalment acceptat d'aquesta reacció està basat en l'esquema proposat per Haver-hi en 1898, en el qual la reacció pot transcórrer per dues rutes, la directa i la de condensació. En aquest capítol explorem totes dues rutes, i observem que la ruptura dels enllaços N-O i la conseqüent formació d'enllaços metall-O està més afavorida que la formació d'enllaços N-H en les superfícies Ni(111) i Co(111), a causa del caràcter oxofílico de tots dos metalls. Les etapes més lentes involucren la formació d'enllaços N-H. En les superfícies de metalls nobles com Pt(111) i Pd(111) s'observa el comportament contrari. La superfície Cu(111) és un cas intermedi comparat amb els metalls nobles i no nobles. A més, el nitroestireno interactua amb els àtoms de Cu de la superfície sol a través de grup nitre, amb la qual cosa és un candidat ideal per a aconseguir selectivitats prop del 100%. No obstant això, la superfície Cu(111) no és capaç d'activar la molècula d'H2. En aquest sentit, proposem un catalitzador bimetàl·lic basat en Cu, dopat amb un altre metall capaç d'activar a l'H2, com ara el Pd o el Ni. En els capítols 4 i 5 hem estudiat la reducció catalítica selectiva dels òxids de nitrogen (SCR, en anglés) amb amoníac. Usant mètodes de DFT, hem trobat rutes per a l'oxidació de NO a NO2, nitrits i nitrats amb energies d'activació relativament baixes. També, hem trobat que la reducció de Cu2+ a Cu+ requereix la participació simultània de NO i NH3. Posteriorment, hem estudiat la influència del NH3 en aquest sistema amb mètodes de dinàmica molecular. El NH3 interacciona fortament amb el Cu+ de manera que dues molècules d'aquest gas són suficients per a trencar la coordinació del catió Cu+ amb els oxígens de l'anell 6r, i formar el complex lineal [Cu(NH3)2]+. A més, els cations Cu2+ poden ser estabilitzats fora de la xarxa mitjançant la formació del complex tetraamincobre(II). A causa de la presència dels cations Cu+ i Cu2+ coordinats a la xarxa de la zeolita, apareixen bandes a la regió entre 800-1000 cm-1 de l'espectre infraroig. L'anàlisi de les freqüències IR de diversos models amb Cu+ i Cu2+ coordinats a l'anell 6r, o formant complexos amb amoníac indica que quan els cations Cu+ i Cu2+ estan coordinats als oxígens de l'anell 6r apareixen vibracions entre 830 i 960 cm-1. Freqüències en aquesta zona també s'obtenen en els casos en què NO, NO2, O2 i combinacions de dues d'ells estan adsorbidos en Cu+ i Cu2+. No obstant això, quan els cations Cu+ i Cu2+ estan fora de l'anell (no hi ha enllaços entre els cations de coure i els oxígens de l'anell 6r) no s'obtenen vibracions d'IR en aquesta regió de l'espectre. Aquests resultats indiquen que amb el seguiment de l'espectre IR durant la reacció SCR és possible determinar si els cations Cu+ i Cu2+ estan coordinats o no a l'anell de 6r en les etapes d'oxidació i reducció. Finalment, hem simulat el desplaçament químic de 19F, δiso, en la zeolita sintetitzada RTH. L'anàlisi del δiso dels diferents models utilitzats ens ha permés reconéixer la simetria del material sintetitzat, el qual pertany al grup espacial P1 i la nova cel·la unitat ha sigut confirmada experimentalment per difracció de raigs X. Finalment, hem assignat el senyal experimental que apareix en l'espectre de 19F a -67.2 ppm, al F- localitzat en un lloc T2, el qual és al seu torn la posició més estable. A més, el senyal a -71.8 ppm s'ha assignat a l'anió F- localitzat en un lloc T4.
[EN] In this work, we have studied two heterogeneous catalytic reactions and the localization of the fluoride anion in the as-made RTH framework, synthesized in fluoride medium. The first results, included in chapter 3, correspond to the chemoselective reduction of nitrostyrene on different metal surfaces, i.e, Ni(111), Co(111), Cu(111) and Pd(111). Until very recently, the reduction of the nitro group was explained on the basis of the general mechanism proposed by Haber in 1898 where the reaction can follow two routes, the direct and condensation route. We have explored the relevant elementary steps of both routes and found that because of the oxophilic nature of Ni and Co, the steps involving the dissociation of N-O bonds and formation of metal-O bonds are significantly favored compared with the other steps on both metal surfaces. In addition, the most demanding steps in terms of energy involve the formation of N-H bonds. These findings are in contrast to those of noble metals such as Pt and Pd, where the opposite behavior is observed. The behavior of Cu(111) lies in between the aforementioned cases, and also no chemical bonds between the carbon atoms of the aromatic ring of nitrostyrene and the Cu(111) surface is formed. For this reason, it might be an ideal candidate to achieve nearly 100 % selectivity. However, the Cu(111) surface does not seem to activate the H2 molecule. In this regard, we propose a bimetallic Cu-based catalyst whose surface is doped with atoms of a H2-activating metal, such as Ni or Pd. On another matter, we have also investigated the selective catalytic reduction of nitrogen oxides (SCR-NOx) and the main results are presented in the following two chapters, 4 and 5. By using static DFT methods, we found pathways for the oxidation of NO to NO2, nitrites and nitrates with relatively low activation energies. We also found, in agreement with experimental reports, that the reduction of Cu2+ to Cu+ requires the simultaneous participation of NO and NH3. Later, molecular dynamics simulations allowed us to assess the influence of NH3. The strong interaction of NH3 with the Cu+ cation is evidenced by its ability to detach Cu+ from the zeolite framework and form the mobile linear complex [Cu(NH3)2]+. Cu+ is no longer coordinated to the zeolite framework in the presence of two NH3 molecules. This observation and the fact that the T-O-T vibrations of the framework produce bands in the 800-1000 cm-1 region of the IR spectrum when perturbed by the coordination of Cu+ and Cu2+ cations, indicate that bands in the 800-1000 cm-1 regions should be observed when both copper cations are bonded to the framework oxygens. Finally, we have also studied NMR properties of the as-made pure silica RTH framework, aiming at locating the compensating fluoride anion. The calculation of the 19F chemical shift in different T sites and comparison with the experimental NMR spectra shows that the as-made RTH belongs to the P-1 space group with 16 Si, 32 O atoms, one fluoride anion and one OSDA cation. These results have been confirmed experimentally by XRD. In addition, we have assigned the experimental signal of 19F at -67.2 ppm to the fluoride anion in a T2 site, which in turn is the most stable location found, and the signal of -71.8 ppm to a fluoride anion sitting in a T4 site.
My acknowledgements to “La Caixa foundation” for the financial support through “La Caixa−Severo Ochoa” International PhD Fellowships (call 2015), to the Spanish Supercomputing Network (RES), to the Centre de Càlcul de la Universitat de València, to the Flemish Supercomputer Center (VSC) of Ghent University for the computational resources and technical support, and to the Spanish Government through the MAT2017-82288-C2-1-P programme
Millan Cabrera, R. (2021). Computational study of heterogeneous catalytic systems. Kinetic and structural insights from Density Functional Theory [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/161934
TESIS

碩士
國立臺灣大學
化學研究所
100
The performance of fuel cell mainly determine by activity of catalyst for fuel decomposition. It’s usually using Pt-based catalyst due to high efficiency. However, Pt is a noble metal; expensive remained a major problem for development fuel cell commercialization. Recent research in cathode catalyst of fuel cell focused on non-noble metal catalyst substitution for Pt-based catalyst, it’s one of solutions to overcome this obstacle. However oxygen reduction reaction (ORR) activity of non-noble metal catalyst is lower than Pt-based catalyst. Thus, improve activity of non-noble metal catalyst become an important issue. Generally, catalytic structure and activity affect by heat treatment which will further influence nitrogen-doped structure in catalyst surface. Different types of nitrogen have different activity for oxygen reduction. Due to the role of heat treatment and carbon support are not fully understood yet, research on these two factors will assist in development fuel cell. In the present study, synthesis catalyst by impregnation method with various heat temperatures in ammonia condition. Used several analytic techniques to optimize synthesis factors and study formation mechanism with 0 dimension and 2 dimension carbon support. Both catalytic series used X-ray powder diffraction to prove crystal structure. X-ray absorption spectroscopy by using synchrotron radiation was applied for oxidation number of iron. Practical size and morphology studied by transmission electron microscopy. X-ray photoelectron spectroscopy characterized structure of nitrogen in catalyst. Surface area analyzer measured specific surface area. ORR and methanol poison tested by cyclic voltammery. Confirm iron nitride of catalyst change with temperature increase. The best ORR activity is Fe2N phase from 700℃ heat treatment. The carbon support dimension induces diverse loading mode, furthermore control practical size and catalytic activity.

碩士
國立聯合大學
化學工程學系碩士班
102
This study aims to develop a suitable non-noble metal of catalyst for proton exchange membrane fuel cell. It used carbon as the support and, used electroless plating to prepare Ni-Co-P alloy catalysts for better catalyst dispersion and reaction activity. To find the best catalyst preparation condition, experimental factors under investigation were：temperature、pH value and concentration of the plating bath, etc. Precious metals salts, such as hexachloroplatinate was then added on the plating bath. These catalysts were expected to have high activity, high corrosion resistance, and low platinum loading. The Ni-Co-P alloy catalyst from this study was examined by FE-SEM for surface morphology, EDS for element analysis, XRD for crystal phase identification, and RDE for electrochemical activity. The catalyst paste was coated on the carbon paper by doctor blade method. The membrane electrode assembly was obtained by laminated membrane and electrodes under proper hot-pressing condition. The performance of this single cell (voltage-current, power-current) was measured. The result suggested that he performance of Ni-Co-P alloy catalysts was obtained by calcination of the electroless plated XC-72R carbon powder. After calcinations of 1 hours at 450℃, the catalyst activity was evaluated by rotating disk electrode with electrode potential scan rate at 5mV/s in 0.5 M sulfuric acid saturated with oxygen. At electrode rotating speed of 900 rpm. The maximum specific current density of 16.58 mA/(cm2‧mg catalyst) was obtained.

碩士
國立臺灣科技大學
材料科學與工程系
103
The growing of greenhouse gases, deteriorating oils and energy issues realize people for the importance of environmental protection. Therefore, the fuel cell is significantly important due to a high efficiency, low pollution and renewable green energy. Fuel cells usually use platinum as catalyst. Unfortunately, the cost of platinum is expensive and it is not economically applied. Moreover, the resources of platinum in the world are getting scarce. Based on this view, the developing of non-noble catalysts become an attractive research topic in recent years. This study attempts to use precursors of nitrogen and sulfur as the dual doping by mixing with iron precursors as non-noble catalyst to replace the platinum catalyst. The prepared catalyst demonstrates good oxygen reduction ability after the pyrolysis with the electron transfer number of 3.99, which is very close to the ideal electron transfer number of 4.00. From the structure analysis, the graphene-like structure is found in the outer layer, which improves the oxygen reduction activity. In XPS spectrum for nitrogen and sulfur analysis, the high amount of pyridinic-N, quaternary-N and thiophene-S structure can significantly enhance the oxygen reduction activity. From XAS analysis, we can understand the bonding of element in the catalyst and speculate catalyst structure. In addition, the catalyst has an excellent stability after 30,000 cycles of stability test. It confirms that dual-doped containing nitrogen and sulfur can enhance the oxygen reduction ability by the synergistic effect.

The key renewable-energy technologies, such as fuel cells, metal-air batteries, and water electrolysers, provide sustainable solution to the aggravating energy and environment issues. They can convert chemical energy to electricity or fuel directly with high efficiency and low even zero greenhouse gas emission. However, the commercial success of these techniques has been greatly hampered by the prohibitive cost, low abundance, and limited stability of the state-of-the-art noble-metal electrocatalysts (Pt, IrO₂ or RuO₂) at the anodes and/or cathodes. Therefore, the development of cost-effective, highly active, and durable electrocatalysts is highly desirable for these techniques. This thesis aims to design and fabricate a series of advanced electrocatalysts for oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and oxygen evolution reaction (OER) which are the cathodic or anodic reactions of fuel cells, metalair batteries and water electrolysers. The first part of the thesis focuses on ORR to fabricate a number of low cost transition metal oxides and carbon materials as the alternative to commercial Pt/C. Non-precious metal oxides such as Mn₃O₄ have been studied as Pt substitute due to their earth abundance and environmental compatibility. In addition, heteroatom-doped graphene which combines excellent electrical conductivity, high surface area, and rich active sites, displays good electrocatalytic performance. As a consequence, a hybrid material composed of Mn₃O₄ nanoparticles on nitrogen-doped graphene was firstly synthesized for ORR catalysis. Further, the shape effect of metal oxide nanoparticles (Mn₃O₄) on ORR activity has been examined, based on the fact that the heterogeneous ORR process involving the adsorption of reactants and desorption of products on the exposed facets of nanocrystals. The second part of thesis is to study HER which is the primary step of sustainable H₂ production from electrochemical water splitting. Other than tuning the chemical composition and nanostructure of electrocatalysts, the HER performance can also be optimized through the manipulation of the electrode architectures. Heteroatom-doped graphene has been investigated as the HER catalyst, but its performance is limited due to the small amount of accessible active sites. In response, we hybridizes heteroatom-doped graphene with a highly active HER catalyst (porous C₃N₄ and 1T-WS₂) into three dimensional flexible hybrid film, which can be directly utilized as HER catalyst electrodes without substrates or binders. This new category of electrocatalysts can combine the facile HER kinetics and high HER activity. This work offers the possibility to tackle the bottleneck of HER electrocatalyst by tailoring the electrocatalytic performance at atomic scale. The third part of thesis aims to design a bifunctional electrocatalyst for both HER and OER. The cobalt oxides are known as an efficient OER electrocatalyst, while cobalt phosphides are active HER electrocatalysts. Through adjusting the anion percentage of P and O elements in cobalt phosphoric oxides, we can obtain the optimized bifunctional catalyst for both HER and OER for overall water electrolysis. Moreover, the cation in cobalt phosphoric oxide is modulated by doping different amount of Fe, which can improve its water splitting ability further. As expected, the obtained catalyst electrode has displayed a superior water electrolysis performance, exhibiting the low driving potential and facile reaction kinetics, which might be associated with the three-dimensional conductive network beneficial for the electron and charge transportation, high accessibility of active sites, and the optimum cation and anion percentages.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2016.

Liquid organic chemical hydride is a promising candidate for hydrogen storage and transport. Methylcyclohexane (MCH) to toluene (TOL) cycle has been considered as one of the feasible hydrogen carrier systems, but selective dehydrogenation of MCH to TOL has only been achieved using the noble Pt-based catalysts. The aim of this study is to develop non-noble, cost-effective metal catalysts that can show excellent catalytic performance, mainly maintaining high TOL selectivity achievable by Pt based catalysts. Mono-metallic Ni based catalyst is a well-known dehydrogenation catalyst, but the major drawback with Ni is its hydrogenolysis activity to cleave C-C bonds, which leads to inferior selectivity towards dehydrogenation of MCH to TOL. This study elucidate addition of the second metal to Ni based catalyst to improve the TOL selectivity. Herein, ubiquitous bi-metallic nanoparticles catalysts were investigated including (Ni–M, M: Ag, Zn, Sn or In) based catalysts. Among the catalysts investigated, the high TOL selectivity (> 99%) at low conversions was achieved effectively using the supported NiZn catalyst under flow of excess H2. In this work, a combined study of experimental and computational approaches was conducted to determine the main role of Zn over Ni based catalyst in promoting the TOL selectivity. A kinetic study using mono- and bimetallic Ni based catalysts was conducted to elucidate reaction mechanism and site requirement for MCH dehydrogenation reaction. The impact of different reaction conditions (feed compositions, temperature, space velocity and stability) and catalyst properties were evaluated. This study elucidates a distinctive mechanism of MCH dehydrogenation to TOL reaction over the Ni-based catalysts. Distinctive from Pt catalyst, a nearly positive half order with respect to H2 pressure was obtained for mono- and bi-metallic Ni based catalysts. This kinetic data was consistent with rate determining step as (somewhat paradoxically) hydrogenation of strongly chemisorbed intermediate originating from TOL. DFT calculation indicated that Zn metal prefers to occupy the step sites of Ni where unselective C–C bond breaking was considered to preferentially occur, explaining suppression of hydrogenolysis activity. Additionally, it confirmed that the H-deficient species at methyl position group (C6H5CH2) was stable on the surface, making its hydrogenation being rate determining step, consistent with positive order in H2 pressure on TOL formation rate. This may explain the conclusive role by H2 in facilitating desorption of the H-deficient surface species that was produced through further dehydrogenation of TOL.

碩士
國立交通大學
環境工程系所
106
For automotive emission control, CO and HCs would be oxidized to CO2 and H2O while NOx would be reduced to N2. The catalysts are referred as three-way catalysts (TWCs) since they can simultaneously remove three different types of air pollutants (CO, HCs and NOx). However, whether these three pollutants are interact at the same time or not, and also the relationship of redox reaction between these three pollutants were still not clear in the past research. On the other hand, due to the well-defined crystalline structure and high thermal stability, perovskite-type oxides (ABO3) have high potential for vehicle emission control catalysts. The commercial TWCs usually employ precious metals as the activated species. But in order to reduce the catalysts costs non-noble metals were selected and the characteristics of each metal were clarified in this study. In this study La, Ce or Sr were selected as the A site, while the B site was considered to be Mn, Fe, Co, Ni or Cu. Perovskite catalysts were prepared by precipitation method and the activities of fresh and thermal aged catalysts were tested in a wide temperature range of 70-450 oC under GHSV of 60,000 h-1. In addition, the physicochemical properties of the products were characterized by XRD, TEM, N2 physisorption measurement and NH3-TPD analysis. The results showed that CeMnO3 catalyst had the best overall performance among all tested catalysts. It has the best NO conversion efficiency of 42% at temperature of 215 oC. In addition, the T50 (temperature at 50% conversion) for C3H8 and CO were 294 oC and 197 oC, respectively; while the T90 for C3H8 and CO were 352 oC and 204 oC, respectively, for fresh CeMnO3 catalyst. Besides, the redox reaction analysis results showed that the increase of O2 concentration tends to increase the NO conversion at high temperature. And the addition of CO reductant can enhance the ability of NO reduction at low temperature.

abstract: Low temperature fuel cells are very attractive energy conversion technology for automotive applications due to their qualities of being clean, quiet, efficient and good peak power densities. However, due to high cost and limited durability and reliability, commercialization of this technology has not been possible as yet. The high fuel cell cost is mostly due to the expensive noble catalyst Pt. Alkaline fuel cell (AFC) systems, have potential to make use of non-noble catalysts and thus, provides with a solution of overall lower cost. Therefore, this issue has been addressed in this thesis work. Hydrogen-oxygen fuel cells using an alkaline anion exchange membrane were prepared and evaluated. Various non-platinum catalyst materials were investigated by fabricating membrane-electrode assemblies (MEAs) using Tokuyama membrane (# A201) and compared with commercial noble metal catalysts. Co and Fe phthalocyanine catalyst materials were synthesized using multi-walled carbon nanotubes (MWCNTs) as support materials. X-ray photoelectron spectroscopic study was conducted in order to examine the surface composition. The electroreduction of oxygen has been investigated on Fe phthalocyanine/MWCNT, Co phthalocyanine/MWCNT and commercial Pt/C catalysts. The oxygen reduction reaction kinetics on these catalyst materials were evaluated using rotating disk electrodes in 0.1 M KOH solution and the current density values were consistently higher for Co phthalocyanine based electrodes compared to Fe phthalocyanine. The fuel cell performance of the MEAs with Co and Fe phthalocyanines and Tanaka Kikinzoku Kogyo Pt/C cathode catalysts were 100, 60 and 120 mW cm-2 using H22 and O2 gases. This thesis also includes work on synthesizing nitrogen doped MWCNTs using post-doping and In-Situ methods. Post-doped N-MWNCTs were prepared through heat treatment with NH4OH as nitrogen source. Characterization was done through fuel cell testing, which gave peak power density ~40mW.cm-2. For In-Situ N-MWCT, pyridine was used as nitrogen source. The sample characterization was done using Raman spectroscopy and RBS, which showed the presence ~3 at.% of nitrogen on the carbon surface.
Dissertation/Thesis
M.S.Tech Technology 2012